I have looked up the data. The Swiss have almost as many weapons as we do, and a murder rate half of that of Australia and England. Norway is another high gun country, and aside from Mr. Brevik, they too have a low murder rate.

Almost as many weapons as in the US?

In 2005 over 10% of Swiss households contained handguns, compared to 18% of U.S. households that contained handguns. In 2005 almost 29% of households in Switzerland contained firearms of some kind, compared to almost 43% in the USA.

That's almost 1.5x as many households containing guns in the USA than in Swizerland and 1.8x as many handguns.

The Swiss do have a relatively large number of firearms compared to other European countries because most men between the ages of 20 and 30 are in the militia and keep their service weapon at home. When they leave they have the choice of retaining their personal weapon. The Swiss government also sponsors training with rifles and shooting in competitions for interested adolescents, both male and female. Competition shooting is very popular in Switzeralnd.

If gun owners in America had to be part of a "well regulated militia," like the Swiss Army is, I think we'd see a drop in gun violence. However Swiss homicide rates are not that low

Switzerland also seems to have more gun crime than you think:

Government statistics for the year 2010 records 40 homicides involving firearms, out of the 53 cases of homicide in 2010.The annual rate of homicide by any means per 100,000 population was 0.70. The annual rate of homicide by guns per 100,000 population was 0.52.

So the Swiss have a much higher rate of Homicide by firearm than the UK (which has much more restricted gun ownership) - but the English seem to be more murderous and must use other means to commit murder. This at least cuts out most mass killings since those are almost always carried out with firearms.

The USA is way above both countries in the overall homicide rate and homicide by firearms rate.